2021-May-11 - Prerelease - 2.6.170

Fix memory leak caused by retained TripleAFrames. (#9213)

I noticed my TripleA was taking a lot of memory and took a heap
dump with JVisualVM. Most of the memory was byte arrays which
were backing Tiles in TileManager. But tracing their referenced,
I noticed I had lots of different TripleAframe instances around,
from games that were closed.

Turns out these were leaking. There were two problems:
  - TripleAframe wasn't being disposed on close.
  - ProMetricsUtils held a static that ended up with an eventual
    transitive reference to TripleAFrame.

Fixing both of these made the TripleAFrame instance disappear
from the heap dump once a game was closed. I'm simply removing
the ProMetricsUtils class since it was just being used for some
debug logging.